Molding processes are known in which fibers are combined with a thermosetting resin and a catalyst and placed in a mold tool to be pressure formed under heat. U.S. Pat. Nos. 4,035,121 and 4,102,963 disclose two different machines for combining resin and fibers in an air laid web structure.
In use, the uniformity of the mat of Web material formed by the '121 patent has been found to be dependent on the level of the fiber maintained in the fiber feed section of the machine. The level of the fiber in the feeder will cause the amount of fiber fed by an elevating apron to vary in the longitudinal flow or mat direction as the fiber feed level changes. In one form of commercially available machine the fiber from the elevator apron is directed through an air bridge which feeds fibers along a horizontal reach to a first perforated evacuated surface to form a feed mat. If the vacuum on the perforated surface is too low, and if the fiber level in the feed section is too great, an excessive amount of fiber will build up in the upstream end of the air bridge. The excess fiber not taken by the air bridge must be fed back into the feeder by a separate top stripper. The result is a system which requires adjustment of multiple variables including feed bin level; vacuum level; top stripper speed and the speed of the elevator apron. The large number of variables makes it difficult to form a feed mat of uniform density. Consequently, subsequent separation of fibers from the feed mat and subsequent final mat build up will not be uniform.
Many final web former structures include a lickerin cylinder located a fixed short distance from a web condenser for forming an air laid web. One example of such a final web former structure is shown in U.S. Pat. No. 3,918,126. The short distance is provided in an attempt to reduce the horizontal reach of the discharge duct from the lickerin. Nevertheless, the horizontal reach will tend to produce differential separation of different density fibers as they are carried through the duct by primary carrier gas. Also, such short distance relationship causes the final mat to develop as a series of shingles formed at approximately 50 degrees to 60 degrees in the direction that the fibers are formed onto the evacuated perforated surface of a final mat forming condenser.
The shingle effect produces weakened sections in web densities in the 35 to 80 oz. per square yard mat weight range, e.g., the higher the mat weight, the more pronounced is the shingle effect. Such weakened sections make it difficult to roll or otherwise handle the final mat without separation at the weakened sections.
In the past it has been necessary to consolidate weakened sections by use of a compaction oven in which the weakened sections are consolidated and fused using low melt thermoplastic fibers or entrained thermoplastic powders to hold the mat sections together. Optionally, such weakened mat sections can be given greater integrity by use of needle looms which knit the weakened fibers together for handling strength. Machines of this type require maintenance to the needles and adjustment of other variables, but does produce a final mat structure that is easily handled by the molder.
Other air laid web machines address velocity differentiation of different density fibers by use of structure designed to produce a uniform air flow velocity for carrying the fibers to the perforated evacuated surfaces for forming the final mat product. One such machine is shown in U.S. Pat. No. 3,949,035 wherein multiple air streams include a primary air stream, a secondary air stream as well as a process air stream. Each stream must be adjusted one to the other to obtain a desired final mat build-up. U.S. Pat. No. 4,264,290 discloses another machine to produce uniform velocity carrying gas streams. The '290 machine requires use of flow reversing inductors to stabilize velocity, Which can produce a flocking or build up of individual fibers prior to deposition on the evacuated perforated surface of a final web condenser. U.S. Pat. No. 4,350,482 discloses an air flow system for production of fibrous sheet material in which a uniform velocity front is maintained by a plurality of louver type vanes which are adjusted in accordance with the amount of fibers carried by the process stream.
Other air lay web apparatus is known for combining different types of fibers into the final mat structure. Such apparatus are shown in U.S. Pat. Nos. 3,781,150 and 3,984,898 both of which combine short and long fiber to form a final mat product.